Re: [PATCH slab/for-next-fixes v3 0/4] mm/slab: fix unbounded recursion in free path with memalloc profiling

[Harry Yoo]

On 7/17/26 3:05 AM, Shakeel Butt wrote:
> On Mon, Jul 13, 2026 at 11:28:48PM +0900, Harry Yoo (Oracle) wrote:
>> This is a follow-up fix after the recent discussion [1].
>> See patch 4 for the detailed description on the bug.
>>
>> Based on slab/for-next-fixes (af9ea231c0b45) and is available at
>> git.kernel.org [2].
>>
>> Instead preventing cycles by bumping up the allocation size of obj_exts
>> arrays, it introduces a new kmalloc type called KMALLOC_NO_OBJ_EXT and
>> disallow formation of cycles between kmalloc types when allocating
>> obj_exts arrays. obj_exts arrays of normal kmalloc caches are served
>> from KMALLOC_NO_OBJ_EXT caches (that don't have obj_exts), and all other
>> obj_exts arrays are served from normal kmalloc caches.
>>
>> I tried to reuse SLAB_ALLOC_NO_RECURSE to make kmalloc_slab() select
>> KMALLOC_NO_OBJ_EXT, but it was not great because it does not allow
>> sheaves for those caches. So I introduced a new slab alloc flag
>> SLAB_ALLOC_NO_OBJ_EXT.
>>
>> To avoid huge confusion, I had to decouple "disallowing sheaves"
>> semantics from SLAB_NO_OBJ_EXT and introduced SLAB_NO_SHEAVES.
>>
>> While this cannot be directly backported to v6.18 and v6.12 due to lack
>> of SLAB_ALLOC_* flags and kmalloc_flags(), I don't this will be
>> particularily challenging to backport it. Instead of a new slab alloc
>> flag, we can use __GFP_NO_OBJ_EXT to select KMALLOC_NO_OBJ_EXT as
>> kmalloc caches don't have sheaves in v6.18 anyway.
> 
> Hi Harry,

Hi Shakeel,

> are you planning to send the backports to stable once this merges into
> linus tree?

If somebody wants to give it a try, that would be great! Otherwise I
will send backports although it might take some time as I'll be
working on and off for a while :)

-- 
Cheers,
Harry / Hyeonggon

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